How to add another dropdown dynamically?

I have a list of spare parts in a dropdown. So a user selects 1 part and inputs an amount desired in a separate text box. 

But how do I offer an option for the user to be able to add an extra dropdown and text box if he desires to order 1 more part from my store?

it would be something like Dynamic fields plugin but for dropdown menus.

thanks

You can use conditional formatting to show a second drop down menu in case needed. Like so:

http://form.jotform.co/form/40876388761873

To create the condition: On the top toolbar click on the Conditions icon, then choose Show /Hide a form field:

My condition basically states that if the user answer Yes to the Question "Do you want to add another item" then the second dropdown field will be shown:

Do let us know if you need further assistance. Thank you.